All the recorded trajectories
are shown in Fig. REF (a)
where the position \(x\)  is plotted versus the angle \(\theta \) , which is the orientation of the squirmer relative to the upper wall normal.
For
strongly
negative \(\beta \)  values (strong pushers) the squirmer tends to orient perpendicular to the walls (shown for \(\beta =-3\)  in Fig. REF (a)).
This is also sketched in Fig. REF (b).
Increasing \(\beta \)  above a certain value induces oscillations of the swimmer between the walls: The squirmer hits a surface, spends some time there, reorients away from the surface, hits the second surface and so on (shown for \(\beta =-1.5\)  in Fig. REF (a) and sketched in Fig. REF (c)).
A
neutral squirmer
still performs oscillations but mainly avoids touching the walls
by swimming with an orientation performing small oscillations about \(\theta =\pi /2\)  along the bounding walls, see also Fig. REF (d).
In contrast, pullers (\(\beta >0\) ) swim stable between the two walls, as sketched in Fig. REF (e). Interestingly, the
\(\beta \) -dependent
dynamics can be captured by considering the lubrication approximation of a squirmer in front of a wall [1]}, [2]}, which predicts the correct dynamics for all considered \(\beta \)  values [3]}.
